The invention relates to the use of hydroxypropyl methyl cellulose ethers for thickening an organic liquid or a mixture of an organic liquid with water. Furthermore, the invention relates to thickened organic liquids or mixtures thereof with water which comprise hydroxypropyl methyl cellulose ethers as thickening agents.
Hydroxypropyl methyl cellulose ethers (HPMC ethers) have been known for a long time and have found wide acceptance for many applications, for example as suspension stabilizers for polymerisation reactions and thickeners in aqeous systems. A process for preparing them is for example described in U.S. Pat. No. 2,949,452.
From U.S. Pat. No. 3,388,082 water soluble HPMC ethers are known which have a methoxyl degree of substitution (DS) of from 0.4 to 1.3, a hydroxypropyl molar substitution (MS) of from 0.2 to 1.4 and a total molar substitution of at least 1.0. The DS/MS values of 0.4/0.2; 0.4/1.4; 1.3/0.2 and 1.3/1.4 can be calculated as percent of methoxyl substitution/hydroxypropoxyl substition. The corresponding weight percent values are 7%/8.3%; 4.8%/43%; 21%/7.8% and 15.2%/40.8% respectively. HPMC ethers which have a methoxyl substitution of from 27% to 30% and a hydroxypropoxyl substitution of from 4% to 7.5%, HPMC ethers which have a methoxyl substitution of from 28% to 30% and a hydroxypropoxyl substitution of from 7% to 12%, HPMC ethers which have a methoxyl substitution of from 19% to 24% and a hydroxypropoxyl substitution of from 4% to 12% and HPMC ethers which have a methoxyl substitution of from 16.5% to 20% and a hydroxypropoxyl substitution of from 23% to 30% are commercially available. These hydroxypropyl methyl cellulose ethers are wellknown as thickeners. While these cellulose ethers are useful in aqueous systems, unfortunately their use in organic liquids is limited because of their limited solubility in many organic solvents. However, the thickening of organic liquids, optionally containing water, is often desirable for a variety of reasons such as to impart consistency (e.g. to gel alcohol fuel), to control rheology of and to provide adhesion to a substrate e.g. in paint remover formulations and to impart workability to non-aqueous mineral binder/filler systems (e.g. gypsum bandages).
In U.S. Pat. No. 3,617,588 a preparation of cellulose ether films, for example pharmaceutical capsule shells, is disclosed. The cellulose ethers are C.sub.2-4 hydroxyalkyl C.sub.1-2 alkyl cellulose ethers which have a DS of 0.6 to 2.0 and a MS of 0.07 to 1.0 and which are characterised by a viscosity of 2-20 mPa.multidot.s as a 2 weight percent aqueous solution at 20.degree. C. Specifically HPMC ethers are disclosed which have DS of 1.8 to 2 and a MS of 0.15 to 0.35 which corresponds to a methoxyl substitution of 28% to 31% and a hydroxypropoxyl substitution of 6% to 13%. U.S. Pat. No. 3,493,407 discloses a process for preparing medical capsules from a solution of HPMC ethers with a methoxyl content of 18 to 32 weight percent and a hydroxypropyl content of 4 to 15 weight percent and which is characterised by a viscosity of 2 to 20 mPa.multidot.s as a 2 weight percent aqueous solution at 20.degree. C. Unfortunately, these HPMC ethers are not very useful as thickeners since a very large amount of HPMC is required to obtain a substantial thickening effect.
In view of the deficiencies of the above mentioned HPMC ethers which are presently known as thickening agents it is highly desirable to provide new HPMC thickening agents for organic liquids.
A useful thickening agent of the HPMC ether type for organic solvents is disclosed in U.S. Pat. No. 3,839,319. The HPMC ethers have a DS of 0.2 to 1.0 and a MS of at least 1.5. The hydroxypropoxyl substitution of such HPMC ethers, expressed as weight percent, is more than 40%. Unfortunately, production on large scale has shown that the HPMC ethers of such a high hydroxypropoxyl substitution are difficult to be dried by application of heat since these HPMC ethers have thermoplastic properties. Generally heat-drying is however preferred. Accordngly it still remains highly desirable to provide a further class of HPMC ethers which are useful for thickening organic liquids.